Men’s Sexual Anatomy: 1 The penis and scrotum

This section describes the visible parts which make up a man’s sexual organs: the penis and scrotum.

Penile anatomy

There are actually quite a lot of parts which have to work together smoothly to make sex possible and satisfying. Knowing a little about these parts will give you more understanding of your own body and how your sexual response works.

The Penis – Anatomy

Looking at it, one can distinguish a long shaft with a tip, called the glans, at the end. The shaft and glans are separated by the corona, or coronal rim, which runs like a ring around the penis just at the base of the glans.

From soft to erect in 30 seconds

On the underside, the corona is traversed by the frenulum, a little piece of skin which joins up the shaft and the foreskin.

This area contains a lot of nerve endings, which makes it one of the most sensitive areas on the penis. The outer skin of the penis, towards the end, normally fits loosely and usually covers the glans of the penis in the flaccid state.

This part of the skin is called the foreskin or prepuce; it is removed during circumcision.

Penile anatomy – intact penis, with no circumcision

At the top of the glans you find the opening of the urethra, through which urine and semen (ejaculatory fluid) are passed to the outside.

The base of the penis is attached in three parts to the internal skeleton and muscles of the hip region. Two suspensory ligaments which run from the base of the penis to the internal structure of the hip help to keep the penis at an upright angle when it’s erect.

The inside of the penis mostly consists of three spongy bodies, which run parallel to each other down the whole length of the penis. During an erection, these spongy areas fill with blood and allow the penis to go hard.

If you look at a cross section of the penis, the two major spongy bodies are called the corpora cavernosa, or cavernous bodies. They lie side by side. Along their underside runs the third spongy body, the corpus spongiosum.

This spongy area is thinner, but through its length runs the urethra, the tube through which you pass urine. At the tip of the penis, the corpus spongiosum expands to form the whole of the body of the glans.

At the top of the two cavernous bodies run the deep dorsal vein and in the middle of it are the dorsal artery and penile nerves.

Additionally, the cavernosal arteries run along the length of the cavernous bodies, bringing a rich blood supply to the penis.

As an erection results from more blood coming into the penis than going out, all of these blood vessels are essential for the penis to function correctly.

Another essential part of the penis are the membranes which surround each of the spongy bodies and the whole structure.

Each spongy body is surrounded by a fascia, the tunica albuginea. The whole structure of the three spongy bodies is surrounded by the Buck’s fascia.

This layer also contains the deep dorsal vein and the dorsal artery and nerve. Then a third layer holds the penis together, the superficial or Colles fascia, which contains another blood vessel, the superficial dorsal vein.

The Scrotum

The word scrotum literally means bag. It’s the supporting structure which holds the testicles, the organs which produce sperm and testosterone.

The scrotum itself is made up of loose skin, fascia and muscle and it hangs underneath the end of the penis attached to the abdominal wall.

Along its midline runs the raphe (or seam), which shows where, internally, a septum divides the scrotum into two areas, each containing one of the testicles.

The scrotum contains smooth muscle fibers, the dartos muscle, which runs into the smooth subcutaneous muscles of the abdominal wall.

Under certain conditions such as cold temperatures, or during exercise, fear or sexual intercourse, the dartos muscle contracts and pulls the testicles closer to the body.

When it’s warm, or under loose clothing, or in older men, the dartos muscle tends to be more relaxed and the scrotum hangs quite low.

This allows the testicles to be kept away from the body and remain cooler than normal body temperature.

This reduction in temperature is believed to help sperm production. One of the testicles, normally the left one, hangs a bit lower in the scrotum, which makes it easier for a man to walk without squeezing his balls. It’s also quite normal for one testicle to be bigger than the other.

Source for the facts cited in this page:

ABC of Sexual Health (2005) Second edition edited by John M Tomlinson, British Medical Journal Books and Blackwell Publishing.